Rostov. It consists in the superficial separation of normal-appearing epidermis into an erosion, as a result
of the shearing stress produced by sliding a finger on it. It is due to poor adhesion of the epidermal cells
(acantholysis). Hence, it occurs in bullous diseases like pemphigus, but not pemphigoid, where the epidermal
split is much deeper. Still, it is not entirely specific for Pemphigus vulgaris, since it can occur in other active blistering diseases, such as scalded skin syndrome.